Polymer capsule having loaded thereon transition metal particles having excellent water dispersibility and stability, and method for preparing same

ABSTRACT

Provided are a polymer capsule loaded with transition metal particles having excellent water dispersibility and stability, and a method for preparing the same. Specifically, the polymer capsule loaded with transition metal particles according to the present invention includes a surface-modified polymer capsule surface-modified to thereby have a positive zeta potential in a dispersed state in water; and transition metal particles loaded on a surface of the surface-modified polymer capsule. In addition, a method for preparing a polymer capsule loaded with transition metal particles according to the present invention includes a) preparing a polymer capsule; b) surface-modifying the polymer capsule to prepare a polymer capsule having a positive zeta potential in a dispersed state in water; and c) sequentially adding a water-soluble transition metal precursor and a reducing agent to a water dispersion of the surface-modified polymer capsule obtained in step b).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 15/303,710, entitled “POLYMER CAPSULE HAVING LOADED THEREONTRANSITION METAL PARTICLES HAVING EXCELLENT WATER DISPERSIBILITY ANDSTABILITY, AND METHOD FOR PREPARING SAME”, filed on Oct. 12, 2016. U.S.patent application Ser. No. 15/303,710 is a U.S. National Phase ofInternational Patent Application Serial No. PCT/KR2015/003821, entitled“POLYMER CAPSULE HAVING LOADED THEREON TRANSITION METAL PARTICLES HAVINGEXCELLENT WATER DISPERSIBILITY AND STABILITY, AND METHOD FOR PREPARINGSAME,” filed on Apr. 16, 2015. International Patent Application SerialNo. PCT/KR2015/003821 claims priority to Korean Patent Application No.10-2014-0045394, filed on Apr. 16, 2014, and to Korean PatentApplication No. 10-2015-0053065, filed on Apr. 15, 2015. The entirecontents of each of the above-cited applications are hereby incorporatedby reference in their entirety for all purposes.

TECHNICAL FIELD

The present invention relates to a polymer capsule loaded withtransition metal particles, and a method for preparing the same, andmore particularly, to a polymer capsule on which ultra-fine transitionmetal particles are uniformly and homogeneously loaded through a simpleprocess composed of two steps to thereby be chemically bonded, and amethod for preparing the same.

BACKGROUND ART

Metal nanoparticles have received much attention in various fields dueto characteristic properties such as a significantly wide surface areaas compared to volume, a quantum confinement effect, a surface plasmoneffect, and the like.

These properties of the metal nanoparticles are significantly affectedby a size and surface thereof and a supporter, and as the supporter onwhich the metal nanoparticles are loaded, a polymer or dendrimer,silica, metal oxides, and the like, have been mainly used.

Particularly, a structure in which the metal nanoparticles are loaded onthe supporter has been actively studied in a catalyst field, but thereare problems such as a low surface activity, low stability, lowdispersibility, continuous inactivation/leaching of a catalyst, or thelike. As an example, a metal catalyst loaded on mesoporous silica isknown to be significantly unstable and be rapidly inactivated/leached atthe time of a catalytic reaction (R. B. Bedford, U. G. Singh, R. I.Walton, R. T. Williams, S. A. Davis, Chem. Mater. 2005).

Further, research into metal nanoparticles which are stable while havinga catalytic activity in an eco-friendly solvent such as water has beenimportantly considered in a green chemistry field due to environmentaland economical reasons and safety. However, research into catalyticreactions in water using a structure in which nanoparticles are loadedon a supporter has not yet been actively conducted (M. L. Kantam, S.Roy, M. Roy, B. Sreedhar, B. M. Choudary, Adv. Synth. Catal. 2005).

DISCLOSURE Technical Problem

An object of the present invention is to provide a polymer capsuleloaded with transition metal particles having excellent stability andwater dispersibility, on which ultra-fine crystalline transition metalnanoparticles are homogeneously loaded.

Another object of the present invention is to provide a method forpreparing a polymer capsule loaded with transition metal particles.

Technical Solution

In one general aspect, a polymer capsule loaded with transition metalparticles contains: a surface-modified polymer capsule obtained bycopolymerizing a compound represented by the following Chemical Formula1 and a compound represented by the following Chemical Formula 2 witheach other, and surface-modified to thereby have a positive zetapotential in a dispersed state in water; and transition metal particlesloaded on a surface of the surface-modified polymer capsule.

In another general aspect, a method for preparing a polymer capsuleloaded with transition metal particles includes: a) preparing a polymercapsule by copolymerizing a compound represented by the followingChemical Formula 1 and a compound represented by the following ChemicalFormula 2 with each other; b) surface-modifying the polymer capsule toprepare a surface-modified polymer capsule having a positive zetapotential in a dispersed state in water; and c) sequentially adding awater-soluble transition metal precursor and a reducing agent to a waterdispersion of the surface-modified polymer capsule obtained in step b).

(In Chemical Formula 1, X is O, S, or NH, A₁ and A₂ are eachindependently —OR₁, —SR₂, —NHR₃, or —OC(═O)R₄, R₁ to R₄ being eachindependently a substituted or unsubstituted (C2-C20)alkenyl group or asubstituted or unsubstituted (C2-C20)alkynyl group, B₁ and B₂ are eachindependently a substituted or unsubstituted (C1-C10)alkylene group, andn is an integer of 4 to 20.)(HS)_(j)—Z—(SH)_(k)  [Chemical Formula 2]

(In Chemical Formula 2, Z is a substituted or unsubstituted(C1-C20)alkylene group, and j and k are each independently an integer of1 to 3).

Advantageous Effects

The polymer capsule loaded with transition metal particles according tothe present invention may have significantly stable water dispersibilityand have a high catalytic activity and recyclability at the time ofbeing used as a catalyst in water

Further, the method for preparing a polymer capsule loaded withtransition metal particles according to the present invention has anadvantage in that the transition metal-polymer capsule in whichmonocrystalline transition metal nanoparticles having an ultra-fine sizeare chemically bound is prepared.

DESCRIPTION OF DRAWINGS

FIG. 1A is a view illustrating particle size distribution, FIGS. 1B and1C are views illustrating scanning electron microscope photographs, andFIGS. 1D and 1E are views illustrating transmission electron microscopephotographs of a surface-modified polymer capsule. In detail, FIG. 1Aillustrates results of measuring particle size distribution of thepolymer capsule (reference numeral 1 in FIG. 1A) synthesized byphotopolymerization and the surface-modified polymer capsule (referencenumber 2 in FIG. 1A) using the dynamic light scattering device(DLS-7000, Otsuka Electronics).

FIG. 2 is a view illustrating a result obtained by measuring particlesize distribution of a surface-modified polymer capsule (indicated byreference numeral 2 in FIG. 2) and a polymer capsule loaded with Pdnanoparticles (indicated by reference numeral 3 in FIG. 2) using adynamic light scattering device (DLS-7000, Otsuka Electronics).

FIGS. 3A and 3D are scanning electron microscope (SEM) photographs of apolymer capsule loaded with Pd nanoparticles, FIGS. 3B and 3E aretransmission electron microscope (TEM) photographs thereof after dyeingwith uranyl acetate, and FIGS. 3C and 3F are high-magnification TEMphotographs thereof.

FIGS. 4A to 4C are views illustrating X-ray photoelectron spectroscopy(XPS) results of a surface-modified polymer capsule, and FIGS. 4D to 4Fare views illustrating XPS results of a polymer capsule loaded with Pdnanoparticles.

FIG. 5 is a view illustrating a scanning TEM image of the polymercapsule loaded with Pd nanoparticles and a fast Fourier transform (FFT)pattern of the Pd nanoparticles.

FIG. 6 is a view illustrating a result obtained by observing C═Ostretching vibration peaks of a surface-modified polymer capsule (2 ofFIG. 6) and a polymer capsule (3 of FIG. 6) loaded with Pd nanoparticlesusing Fourier transform infrared spectroscopy (FT-IR).

FIGS. 7A to 7C are high-magnification TEM photographs of polymercapsules loaded with Pd nanoparticles, and FIGS. 7D to 7F are viewsillustrating results obtained by measuring diameters of the loaded Pdnanoparticles.

FIGS. 8A and 8C are a high-magnification TEM photograph of a preparedpolymer capsule loaded with Au nanoparticles and a view illustrating aresult obtained by measuring a diameter of the loaded transition metalnanoparticles (Au nanoparticles), respectively, and FIGS. 8B and 8D area high-magnification TEM photograph of a polymer capsule loaded with Ptnanoparticles, and a view illustrating a result obtained by measuring adiameter of the loaded transition metal nanoparticles (Ptnanoparticles), respectively.

FIG. 9 is a view illustrating a result obtained by measuring aconversion rate of aryl iodide using the prepared polymer capsule loadedwith Pd nanoparticles depending on a reaction time.

BEST MODE

Hereinafter, a manufacturing method according to the present inventionwill be described in detail with reference to the accompanying drawings.The following accompanying drawings are provided by way of example sothat the idea of the present invention can be sufficiently transferredto those skilled in the art to which the present invention pertains.Therefore, the present invention is not limited to the drawings to beprovided below, but may be modified in different forms. In addition, thedrawings to be provided below may be exaggerated in order to clarify thescope of the present invention. Here, technical terms and scientificterms used in the present specification have the general meaningunderstood by those skilled in the art to which the present inventionpertains unless otherwise defined, and a description for the knownfunction and configuration unnecessarily obscuring the gist of thepresent invention will be omitted in the following description and theaccompanying drawings.

A polymer capsule loaded with transition metal particles according to anexemplary embodiment of the present invention may contain: asurface-modified polymer capsule obtained by copolymerizing a compoundrepresented by the following Chemical Formula 1 and a compoundrepresented by the following Chemical Formula 2 with each other, andsurface-modified to thereby have a positive zeta potential in adispersed state in water; and transition metal particles loaded on asurface of the surface-modified polymer capsule.

The polymer capsule loaded with transition metal particles as describedabove may have excellent stability in the dispersed state in water andhave a high catalytic activity and recyclability at the time of beingused as a catalyst in water.

The compound represented by Chemical Formula 1 according to theexemplary embodiment of the present invention may be a cucurbiturilderivative having the following structure.

In Chemical Formula 1, X is O, S, or NH, A₁ and A₂ are eachindependently —OR₁, —SR₂, —NHR₃, or —OC(═O)R₄, R₁ to R₄ being eachindependently a substituted or unsubstituted (C2-C20)alkenyl group or asubstituted or unsubstituted (C2-C20)alkynyl group, B₁ and B₂ are eachindependently a substituted or unsubstituted (C1-C10)alkylene group, andn is an integer of 4 to 20.

Preferably, in Chemical Formula 1, X may be O, A₁ and A₂ may be eachindependently —OR₁ or —OC(═O)R₄, R₁ to R₄ being each independently asubstituted or unsubstituted (C2-C10)alkenyl group or a substituted orunsubstituted (C2-C10)alkynyl group, B₁ and B₂ may be each independentlya substituted or unsubstituted (C1-C10)alkylene group, and n may be aninteger of 4 to 12.

More preferably, in Chemical Formula 1, X may be O, A₁ and A₂ may beeach independently —OR₁, R₁ being an ethenyl group (—CH—CH₂), a2-propenyl group (—CH₂CH—CH₂), a 3-butenyl group (—CH₂CH₂CH—CH₂), a4-pentenyl group (—CH₂CH₂CH₂CH—CH₂), an ethynyl group (—C≡CH), apropynyl group (—CH₂CCH), a pentynyl group (—CH₂CH₂CH₂CCH), or the like,B₁ and B₂ may be a methylene group (—CH₂—) or an ethylene group(—CH₂CH₂—), and n may be an integer of 4 to 12.

The compound represented by Chemical Formula 2 according to theexemplary embodiment of the present invention, which is a materialforming the polymer capsule together with the compound represented byChemical Formula 1 by copolymerization, may be an aliphatic compoundhaving two or more thiol groups.(HS)_(j)—Z—(SH)_(k)  [Chemical Formula 2]

(In Chemical Formula 2, Z is a substituted or unsubstituted(C1-C20)alkylene group, and j and k are each independently an integer of1 to 3).

Preferably, in Chemical Formula 2, Z is a substituted or unsubstituted(C6-C20)alkylene group, and j and k are each independently an integer of1 to 3.

A specific example of the compound represented by Chemical Formula 2 mayinclude 1,6-hexanedithiol, 1,8-octanedithiol,3,6-dioxa-1,8-octanedithiol, 1,4-dimercaptobutane-2,3-diol,pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropanetris(3-mercaptopropionate), or the like, but is not limited thereto.

Here, unless particularly described in the specification, in ChemicalFormulas 1 and 2, the term “substitution” and “substituted” means thatat least one atom is substituted with one or more substituents selectedfrom the group consisting of oxygen (O), sulfur (S), nitrogen (N),halogen (F, Cl, Br, or I), a hydroxyl group, a ketone group, an estergroup, and the like.

The polymer capsule obtained by copolymerizing the compound representedby Chemical Formula 1 and the compound represented by Chemical Formula 2has a negative zeta potential by a functional group (C═O, S═S, or C═NH)in Chemical Formula 1, and it is possible to allow the polymer capsuleto have a positive zeta potential in the dispersed state in water bysurface-modifying the polymer capsule having the negative zetapotential. The surface-modified polymer capsule may have a zetapotential of 60 to 90 mV in the dispersed state in water, that is, in astate in which a matrix is water.

This positive potential, preferably, the zeta potential of 60 to 90 mVmay improve dispersion stability of the polymer capsule when thetransition metal nanoparticles nucleate and grow on a surface of thepolymer capsule, thereby making it possible to allow transition metalnanoparticles to be uniformly formed on the entire surface of thepolymer capsule.

In detail, the surface-modified polymer capsule may be a polymer capsuleon which a sulfonium group having a positive charge is formed. Sulfur ofthe sulfonium group may voluntarily and strongly bind to a transitionmetal. That is, in the polymer capsule of which the sulfonium group isformed on the surface, a nucleation site of the transition metal may beprovided by the sulfonium group, such that ultra-fine transition metalparticles having an average diameter of 1.5 to 3.5 nm may behomogeneously loaded on the polymer capsule at a uniform size. Inaddition, as the transition metal of the transition metal particles ischemically bound to sulfur of the sulfonium group, the transition metalparticles may be strongly and stably attached to the polymer capsule.

In the polymer capsule on which the transition metal particles areloaded as described above, 0.1 to 12 parts by weight, more preferably 1to 10 parts by weight of a particulate transition metal may be loadedbased on 100 parts by weight of the polymer capsule. As the ultra-finetransition metal particles are loaded on the surface of the polymercapsule at the above-mentioned ratio, the polymer capsule may have ahigh catalytic activity and recyclability at the time of being used asthe catalyst in water.

In this case, the transition metal particles according to the exemplaryembodiment is not particularly limited, but may be formed of one or moreselected from Au, Ag, Pd, and Pt.

A method for preparing a polymer capsule loaded with transition metalparticles as described above may include: a) preparing a polymer capsuleby copolymerizing a compound represented by Chemical Formula 1 and acompound represented by Chemical Formula 2 with each other; b)surface-modifying the polymer capsule to prepare a polymer capsulehaving a positive zeta potential in a dispersed state in water; and c)sequentially adding a water-soluble transition metal precursor and areducing agent to a water dispersion of the surface-modified polymercapsule obtained in step b).

The compound represented by Chemical Formula 1 according to theexemplary embodiment of the present invention may be a cucurbiturilderivative having the following structure.

In Chemical Formula 1, X is O, S, or NH, A₁ and A₂ are eachindependently —OR₁, —SR₂, —NHR₃, or —OC(═O)R₄, R₁ to R₄ being eachindependently a substituted or unsubstituted (C2-C20)alkenyl group or asubstituted or unsubstituted (C2-C20)alkynyl group, B₁ and B₂ are eachindependently a substituted or unsubstituted (C1-C10)alkylene group, andn is an integer of 4 to 20.

Preferably, in Chemical Formula 1, X may be O, A₁ and A₂ may be eachindependently —OR₁ or —OC(═O)R₄, R₁ to R₄ being each independentlysubstituted or unsubstituted (C2-C10)alkenyl or substituted orunsubstituted (C2-C10)alkynyl, B₁ and B₂ may be each independentlysubstituted or unsubstituted (C1-C10)alkylene, and n may be an integerof 4 to 12.

More preferably, in Chemical Formula 1, X may be O, A₁ and A₂ may beeach independently —OR₁, R₁ being an ethenyl group (—CH—CH₂), a2-propenyl group (—CH₂CH—CH₂), a 3-butenyl group (—CH₂CH₂CH—CH₂), a4-pentenyl group (—CH₂CH₂CH₂CH—CH₂), an ethynyl group (—C≡CH), apropynyl group (—CH₂CCH), a pentynyl group (—CH₂CH₂CH₂CCH), or the like,B₁ and B₂ may be a methylene group (—CH₂—) or ethylene group (—CH₂CH₂—),and n may be an integer of 4 to 12.

The compound represented by Chemical Formula 2 according to theexemplary embodiment of the present invention, which is a materialforming the polymer capsule together with the compound represented byChemical Formula 1 by copolymerization, may be an aliphatic compoundhaving two or more thiol groups.(HS)_(j)—Z—(SH)_(k)  [Chemical Formula 2]

(In Chemical Formula 2, Z is a substituted or unsubstituted(C1-C20)alkylene group, and j and k are each independently an integer of1 to 3).

Preferably, in Chemical Formula 2, Z is a substituted or unsubstituted(C6-C20)alkylene group, and j and k are each independently an integer of1 to 3.

A specific example of the compound represented by Chemical Formula 2 mayinclude 1,6-hexanedithiol, 1,8-octanedithiol,3,6-dioxa-1,8-octanedithiol, 1,4-dimercaptobutane-2,3-diol,pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropanetris(3-mercaptopropionate), or the like, but is not limited thereto.

Here, unless particularly described in the specification, in ChemicalFormulas 1 and 2, the term “substitution” and “substituted” means thatat least one atom is substituted with one or more substituents selectedfrom the group consisting of oxygen (O), sulfur (S), nitrogen (N),halogen (F, Cl, Br, or I), a hydroxyl group, a ketone group, an estergroup, and the like.

The polymer capsule may be prepared by a copolymerization reactionbetween the compound represented by Chemical Formula 1 and the compoundrepresented by Chemical Formula 2, in detail, a photopolymerizationreaction between the compound represented by Chemical Formula 1, having3 to 20 ethenyl groups (—CH—CH₂) or ethynyl group (—C≡CH) and thecompound represented by Chemical Formula 2, having two or more thiolgroups. This reaction is a reaction known in the art as a thiol-enephotopolymerization reaction (Macromolecules, 2002, 35, 5361;Macromolecules, 2003, 36, 4631).

More specifically, step a) may include dissolving the compoundrepresented by Chemical Formula 1 and the compound represented byChemical Formula 2 in an organic solvent; preparing the polymer capsuleby copolymerizing the compound represented by Chemical Formula 1 and thecompound represented by Chemical Formula 2 through light irradiation;and removing residues using dialysis. As the organic solvent used instep a), any solvent may be used as long as the compound represented byChemical Formula 1 and the compound represented by Chemical Formula 2are dissolved therein. As a specific example, one or more solventsselected from chloroform, methyl alcohol, ethyl alcohol, dimethylsulfoxide, dichloromethane, dimethylformamide, tetrahydrofuran, acetone,and acetonitrile may be used. At the time of light irradiation,ultraviolet (UV) light, specifically, UV light in a wavelength range of254 to 300 nm may be irradiated for 5 to 8 hours, thereby making itpossible to copolymerize the compound represented by Chemical Formula 1and the compound represented by Chemical Formula 2. At the time of thecopolymerization reaction, a radical initiator may be added to thesolution in which the compound represented by Chemical Formula 1 andcompound represented by Chemical Formula 2 are dissolved beforeirradiating the UV light, and the copolymerization reaction may befurther promoted by the radical initiator as described above. As theradical initiator, any radical initiator may be used as long as it isknown to be used in the thiol-ene photopolymerization reaction. As aspecific example, the radical initiator may be one or more selected fromAlBN, K₂S₂O₈, (NH₄)₂S₂O₈, and benzoyl peroxide, but is not limitedthereto.

In step a), an excessive amount of the compound represented by ChemicalFormula 2 may be used as compared to the compound represented byChemical Formula 1. For example, a molar ratio of the compoundrepresented by Chemical Formula 1 to the compound represented byChemical Formula 2 may be 1:40 to 60, but is not limited thereto. Thepolymer capsule is prepared by polymerizing the compound represented byChemical Formula 1 and the compound represented by Chemical Formula 2using the thiol-ene photopolymerization reaction as described above,wherein the compound represented by Chemical Formula 2 may be added inan amount of 40 to 60 moles based on 1 mole of the compound representedby Chemical Formula 1. That is, after dissolving the compoundrepresented by Chemical Formula 1 and the compound represented byChemical Formula 2 in the organic solvent so that the amount of thecompound represented by Chemical Formula 2 is 40 to 60 moles based on 1mole of the compound represented by Chemical Formula 1, the light may beirradiated.

Protrusions of a disulfide loop may be formed on a surface of acopolymer capsule by adding the compound represented by Chemical Formula2 in a significantly excessive amount based on the compound representedby Chemical Formula 1, and this disulfide loop may serve as dithiolsources capable of strongly binding to the transition metalnanoparticles. Preferably, the light may be irradiated after dissolvingthe compound represented by Chemical Formula 1 and the compoundrepresented by Chemical Formula 2 so that the amount of the compoundrepresented by Chemical Formula 2 is 45 to 55 moles based on 1 mole ofthe compound represented by Chemical Formula 1. In this range, thethiol-ene photopolymerization reaction may be smoothly carried out, andat the same time, it is possible to prevent activity of the transitionmetal nanoparticles from being deteriorated by significantly excessivedisulfide loop.

Hereinafter, unless particularly described, the polymer capsule preparedby polymerization of the compound represented by Chemical Formula 1 andthe compound represented by Chemical Formula 2 in step a) is entirelyused as a raw material of surface-modification, and the surface-modifiedpolymer capsule may be entirely dispersed in water to thereby beprepared as the water dispersion of the surface-modified polymercapsule.

The polymer capsule prepared by copolymerization of the compoundrepresented by Chemical Formula 1 and the compound represented byChemical Formula 2 may be used as a carrier on which the transitionmetal nanoparticles are loaded.

When the polymer capsule is prepared by polymerizing the compoundrepresented by Chemical Formula 1 and the compound represented byChemical Formula 2 using the thiol-ene photopolymerization reaction instep a), the polymer capsule has a negative zeta potential by the C═O,C═S, or C═NH functional group in Chemical Formula 1.

In step b), the polymer capsule may be surface-modified so as to have apositive zeta potential in the dispersed state in water, that is, astate in which a matrix is water.

Surface-modification may be performed using a surface-modifier allowinga surface of the prepared polymer capsule to have a positive charge sothat the polymer capsule has a zeta potential of 60 to 90 mV in thestate in which the matrix is water.

This positive potential, preferably, the zeta potential of 60 to 90 mVmay improve dispersion stability of the polymer capsule when thetransition metal nanoparticles nucleate and grow on the surface of thepolymer capsule in step c), thereby making it possible to allowtransition metal nanoparticles to be uniformly formed on the entiresurface of the polymer capsule.

Further, the positive potential, preferably, the zeta potential of 60 to90 mV may enable to stable and uniform supply a material (supply of atransition metal source) to the polymer capsule at the time ofnucleation and growth of the transition metal by a reducing agent inaddition to improving the dispersion stability as described above. Indetail, as described below, it is preferable that a water-solubletransition metal precursor is an alkali metal-transition metal halide.The reason is that the water-soluble transition metal precursor may bedissociated into an alkali metal cation and a transition metal halideanion in a water phase. Therefore, the transition metal added to thewater dispersion of the polymer capsule before being reduced by thereducing agent may exist as the transition metal halide anion. In thecase in which the surface of the polymer capsule is surface-modified soas to have a positive potential, preferably, a potential of 60 to 90 mV,the transition metal halide anions may uniformly enclose around thepolymer capsule by electrostatic force between the polymer capsulehaving the positive charge and the transition metal halide having thenegative charge, and while the nucleation and growth of the transitionmetal on the surface of the polymer capsule occur by the reducing agent,the transition metal source may be stably supplied to the surface of thepolymer capsule in the water phase.

In the method for preparing a polymer capsule according to the exemplaryembodiment of the present invention, it is preferable that thesurface-modification is performed using alkyl halide. That is, it ispreferable that the copolymer capsule obtained in step a) issurface-modified using the alkyl halide as the surface-modifier.

The alkyl halide may change a thioether unit into a sulfonium group bypartially alkylating the thioether unit existing in the copolymercapsule obtained in step a). Therefore, the sulfonium group having apositive charge may be formed on the surface of the copolymer capsule,and sulfur of the sulfonium group may voluntarily and strongly bind tothe transition metal. That is, in the copolymer capsule surface-modifiedso that the sulfonium group is formed by the alkyl halide, a nucleationsite of the transition metal may be provided by the sulfonium group,such that ultra-fine transition metal particles having an averagediameter of 1.5 to 3.5 nm may be homogeneously loaded on the copolymercapsule at a uniform size, and as the transition metal of the transitionmetal particles is chemically bound to sulfur of the sulfonium group,the transition metal particles are strongly and stably attached to thecopolymer capsule.

The alkyl halide may be, for example, (C1-C6)alkyl halide, but is notlimited thereto. In more detail, the alkyl halide may be one or moreselected from (C1-C6)alkyl chloride, (C1-C6)alkyl iodide, (C1-C6)alkylbromide, and (C1-C6)alkyl fluoride. It is preferable that the alkylhalide is alkyl iodide so as to be capable of selectively alkylatingthioether unit and allowing the surface of the polymer capsule to bepositively charged to thereby improve water dispersibility and bindingcapacity to the transition metal. Further, alkyl of the alkyl halide maybe (C1-C6)alkyl, preferably, (C1 to C4)alkyl, more preferably(C1-C2)alkyl, and most preferably, methyl. The reason is that the longerthe alkyl, the lower the affinity to water, such that waterdispersibility and stability of the modified polymer capsule may bedeteriorated.

In detail, step b) may include b1) adding the surface-modifier to adispersion in which the polymer capsule obtained in step a) is dispersedin alcohol and performing incubation; and b2) obtaining the waterdispersion of the surface-modified polymer capsule by purification usingdialysis. In this case, the alcohol may be (C1-C4) lower alcohol, andincubation may be performed for 0.5 to 2 days.

A significantly excessive amount of the surface-modifier may be addedbased on a total number of moles of the compound represented by ChemicalFormula 1, that is, a total number of moles of the compound representedby Chemical Formula 1, used in step a). As a specific example, theamount of surface modifier may be 400 to 600 times based on the totalnumber of moles of the compound represented by Chemical Formula 1.Further, as described above, the (C1-C6)alkyl halide, preferably,(C1-C6)alkyl iodide, and most preferably methyl iodide (CH₃I) is used asthe surface-modifier, such that the thioether unit of the surface of thepolymer capsule may be selectively and partially alkylated by a methodof contacting the surface-modifier and the polymer capsule through aliquid matrix at room temperature for a long period of time.

Thereafter, the polymer capsule loaded with the transition metalnanoparticles may be prepared by sequentially adding the water-solubletransition metal precursor and the reducing agent to the waterdispersion of the surface-modified polymer capsule obtained in step b).

It is preferable that the water-soluble transition metal precursor addedto the water dispersion of the surface-modified polymer capsule is aprecursor containing a transition metal anion among cations and anionsformed by dissociation of transition metal precursors in water.Therefore, supply of the material may be smoothly performed as describedabove, and the transition metal nanoparticles may be selectively formedon the surface-modified polymer capsule. In detail, it is preferablethat the water-soluble transition metal precursor is alkalimetal-transition metal halide. An alkali metal of the alkalimetal-transition metal halide may be one or more selected from sodium,potassium, and lithium. The alkali metal-transition metal halide may beone or more selected from chloride, iodide, bromide, and fluoride. Atransition metal of the alkali metal-transition metal halide may be atransition metal to be loaded on the copolymer capsule. As a specificexample, the transition metal may be one or more selected from Au, Ag,Pd, and Pt.

An average size of the transition metal nanoparticles loaded and boundto the polymer capsule may be adjusted by an addition amount of thewater-soluble transition metal precursor added to the water dispersionof the surface-modified polymer capsule. Here, in the case in which anexcessive amount of the water-soluble transition metal precursor isadded to the water dispersion, there is a risk that the polymer capsuleswill be aggregated with each other by a reduced transition metal or acoating layer of the transition metal instead of independent particleswill be formed. Therefore, it is preferable that the number of moles ofthe water-soluble transition metal precursor added to the waterdispersion of the surface-modified polymer capsule is 1 to 4 times basedon the total number of moles of the compound represented by ChemicalFormula 1 in step a).

As described above, the ultra-fine monocrystalline transition metalparticles having a significantly uniform size may be bound to thepolymer capsule by adding the water-soluble transition metal precursorso as to satisfy the above-mentioned molar ratio and sequentially addingthe reducing agent while providing the nucleation site of the transitionmetal by surface-modifying the surface of the polymer capsule so as tohave the positive zeta potential using the alkyl halide, preferably,alkyl iodide, and most preferably, methyl iodide as the surface-modifierand forming the sulfonium group on the surface.

It is preferable that the reducing agent added to the water dispersionof the surface-modified polymer capsule is a strong reducing agentcapable of rapidly reducing the water-soluble transition metal precursorwithout affecting the polymer capsule. The reason is that in the case inwhich reducing power is strong, ultra-fine transition metal particlesmay be homogeneously formed using the sulfonium group as the nucleationsite. In view of providing strong reducing power without damaging thepolymer capsule, it is preferable that the reducing agent is NaBH₄,NaOH, or a mixture thereof.

An amount of the reducing agent is not limited as long as the reducingagent may sufficiently reduce the added water-soluble transition metalprecursor. As a specific example, 1 to 20 moles of the reducing agent,preferably, 1 to 20 moles of NaBH₄, NaOH, or the mixture thereof may beadded based on 1 mole of the water-soluble transition metal precursor.It is preferable that the reducing agent is added after an ion layer ofthe transition metal halide anion is formed on a surface region of thepolymer capsule positively charged by dissolution of the water-solubletransition metal precursor, preferably, the alkali metal-transitionmetal halide. As a non-restrictive and specific example, the reducingagent may be added after 1 to 8 hours from dissolution of thewater-soluble transition metal precursor. After adding the reducingagent, room-temperature incubation may be performed for 3 to 8 hours,and then, the polymer capsule loaded with the metal particles may bepurified using dialysis.

Inventive Example

Preparation of Polymer Capsule

43.7 mg (240 μmol) of 3,6-dioxa-1,8-octanedithiol was added to anddissolved in a solution in which 10.4 mg (5.0 μmol) of allyloxycucurbit[6]uril (compound represented by Chemical Formula 3) wasdissolved in methanol (10 ml). After performing nitrogen purging, apolymer capsule dispersed in methanol was prepared by applying UV lightwith wavelengths of 254 nm and 300 nm for 10 hours and then removingresidues by dialysis (Thermo SnakeSkin Pleated Dialysis Tubing, MWCO:10,000). Then, a total of 19.8 mg of a polymer capsule was prepared byvolatilizing and removing methanol.

As a result of dropping a drop of the polymer capsule dispersed inmethanol on a planar substrate, drying the drop, and then observing theformed product using a transmission electron microscope, it wasconfirmed that the polymer capsule has a capsule shape, and as a resultof measuring a diameter of the prepared polymer capsule using a dynamiclight scattering device (DLS-7000, Otsuka Electronics), it was confirmedthat a polymer capsule having an average diameter of 100 nm wasprepared.

As a result of measuring a zeta potential (Zetasizer Nano ZS instrument,Malvern) after dispersing the dried polymer capsule (19.8 mg) in 10 mlof water, it was confirmed that the polymer capsule had a zeta potentialof −13.8±8.7 mV.

Elemental analysis result of the polymer capsule using elementalanalyzer: Calculation value[(C₇₂H₉₆N₂₄O₂₄)(C₆H₁₂O₂S₂)_(9.8)(CH₄O)₃(H₂O)₅]_(n): C, 44.22; H, 6.53;N, 9.25; S, 17.28; Measured value: C, 43.88; H, 6.02; N, 9.19; S, 17.16.

Preparation of Surface-Modified Polymer Capsule

After a total of 19.8 mg of the synthesized polymer capsule wasre-dispersed in 10 ml of methanol, 2.4 mmol of CH₃I corresponding to asurface-modifier was added thereto. After incubation at room temperaturefor one day, 10 ml of a water dispersion of a total of 22.1 mg of asurface-modified polymer capsule was obtained by purification usingdialysis.

Elemental analysis result of the surface-modified polymer capsule usingelemental analyzer: calculation value[(C₇₂HτN₂₄O₂₄)(C₆H₁₂O₂S₂)_(9.3)(CH₃I)₆(H₂O)_(5.5)]_(n): C, 37.34; H,5.54; N, 7.80; S, 13.89; measured value: C, 37.58; H, 5.38; N, 7.58; S,13.51.

As a result of measuring a zeta potential (Zetasizer Nano ZS instrument,Malvern) after dispersing the surface-modified polymer capsule (19.8 mg)in 10 ml of water, it was confirmed that the surface-modified polymercapsule had a zeta potential of 72.9±10.0 mV. It may be appreciatedthrough the elemental analysis and the zeta potential that thioetherexisting on a surface of the polymer capsule was changed into asulfonium group by CH₃I.

FIGS. 1A to 1E are views illustrating particle size distribution,scanning electron microscope photographs, and transmission electronmicroscope photographs of a surface-modified polymer capsule. In detail,FIG. 1A illustrates results of measuring particle size distribution ofthe polymer capsule (reference numeral 1 in FIG. 1A) synthesized byphotopolymerization and the surface-modified polymer capsule (referencenumber 2 in FIG. 1A) using the dynamic light scattering device(DLS-7000, Otsuka Electronics). It may be appreciated that in the caseof the surface-modified polymer capsule, water dispersibility was stablymaintained even after 1 month.

FIGS. 1B and 1C are scanning electron microscope photographs of thesurface-modified polymer capsule and FIGS. 1D and 1E are transmissionelectron microscope photographs of the surface-modified polymer capsule.Transmission electron microscope (TEM) observation was performed afterdyeing with uranyl acetate. As illustrated in FIGS. 1B to 1E, it may beconfirmed that even after surface-modification of the polymer capsule,the shape or size thereof was maintained as it is in a state in whichthe polymer capsule was synthesized.

Preparation of Polymer Capsule Loaded with Pd Nanoparticles

An aqueous K₂PdCl₄ solution was added to 0.5 ml of a water dispersion(containing 0.25 μmol of allyloxy cucurbit[6]uril) in which 1.1 mg ofthe surface-modified polymer capsule was dispersed in water so that 0.75μmol of K₂PdCl₄ was added thereto, and incubated at room temperature for3 hours. Thereafter, an aqueous NaBH₄ solution was added to the waterdispersion so that 12 μmol of NaBH₄ was added thereto, and incubatedagain at room temperature for 5 hours, followed by dialysis, therebypreparing a polymer capsule loaded with Pd nanoparticles.

Here, as a result of measuring a zeta potential of the polymer capsuledispersed in water before adding a reducing agent after adding theaqueous K₂PdCl₄ solution to the water-dispersion, it was confirmed thatthe zeta potential was decreased to 48.4±7.0 mV.

Preparation of Polymer Capsule Loaded with Au Nanoparticles

An aqueous KAuCl₄ solution was added to 0.5 ml of a water dispersion(containing 0.25 μmol of allyloxy cucurbit[6]uril) in which 1.1 mg ofthe surface-modified polymer capsule was dispersed in water so that 0.25μmol of KAuCl₄ was added thereto, and incubated at room temperature for3 hours. Thereafter, an aqueous NaOH solution was added to the waterdispersion so that 4 μmol NaOH was added thereto, and incubated again atroom temperature for 5 hours, followed by dialysis, thereby preparing apolymer capsule loaded with Au nanoparticles.

Preparation of Polymer Capsule Loaded with Pt Nanoparticles

An aqueous K₂PtCl₄ solution was added to 0.5 ml of a water dispersion(containing 0.25 μmol of allyloxy cucurbit[6]uril) in which 1.1 mg ofthe surface-modified polymer capsule was dispersed in water so that 0.5μmol K₂PtCl₄ was added thereto, and incubated at room temperature for 3hours. Thereafter, an aqueous NaBH₄ solution was added to the waterdispersion so that 8 μmol NaBH₄ was added thereto, and incubated againat room temperature for 5 hours, followed by dialysis, thereby preparinga polymer capsule loaded with Pt nanoparticles.

FIG. 2 is a view illustrating a result obtained by measuring particlesize distribution of the surface-modified polymer capsule (indicated byreference numeral 2 in FIG. 2) and the polymer capsule loaded with Pdnanoparticles (indicated by reference numeral 3 in FIG. 2) using adynamic light scattering device (DLS-7000, Otsuka Electronics). It maybe appreciated that after loading the Pd nanoparticles, a polymercapsule having an average diameter of 130 nm was formed.

FIGS. 3A and 3D are scanning electron microscope photographs of apolymer capsule loaded with pd nanoparticles, FIGS. 3B and 3E aretransmission electron microscope photographs thereof after dyeing withuranyl acetate, and FIGS. 3C and 3F are high-magnification transmissionelectron microscope photographs.

As illustrated in FIGS. 3A to 3F, it may be appreciated that the polymercapsule loaded with the transition metal nanoparticles maintained aspherical capsule shape, and ultra-fine and uniform Pd nanoparticleswere uniformly and homogeneously loaded on the surface of the polymercapsule. As a result of transmission electron microscope observation, itwas confirmed that the Pd nanoparticles had a significantly uniform sizeof 1.9±0.2 nm, and as a result of inductively coupled plasma atomicemission spectroscopy (ICP-AES) analysis, it was confirmed that 81% ofPd in the added K₂PdCl₄ was loaded as the Pd nanoparticles.

Further, it was confirmed that water dispersibility of the preparedpolymer capsule loaded with the transition metal nanoparticles was notdeteriorated even after 6 months from a preparation time point.

FIGS. 4A to 4C are views illustrating X-ray photoelectron spectroscopy(XPS) results of the surface-modified polymer capsule, and FIGS. 4D to4F are views illustrating XPS results of the polymer capsule loaded withPd nanoparticles. It may also be appreciated from the XPS results inFIGS. 4A to 4F that the Pd nanoparticles were loaded on the polymercapsule, and it may be appreciated that in the polymer capsule loadedwith the Pd nanoparticles, an oxygen (is) peak shifted to a longwavelength, and a new sulfur (2p) peak of 162.8 eV appeared. Therefore,it may be appreciated that carbonyl oxygen interacted with the Pdnanoparticles, and a Pd—S bond was formed.

FIG. 5 is a view illustrating a scanning transmission electronmicroscope (STEM) image of the polymer capsule loaded with Pdnanoparticles and a fast Fourier transform (FFT) pattern of the Pdnanoparticles. As a result of the observation, it was confirmed that allof the Pd nanoparticles loaded on the polymer capsule weremonocrystalline particles having a (111) face centered cubic (FCC)structure.

As a result obtained by observing C═O stretching vibration peaks of thesurface-modified polymer capsule (black color of FIG. 6) and the polymercapsule (red color of FIG. 6) loaded with Pd nanoparticles using Fouriertransform infrared spectroscopy (FT-IR), it was confirmed that there wasno significant shift as illustrated in FIG. 6.

FIGS. 7A to 7C are high-magnification TEM photographs of polymercapsules loaded with Pd nanoparticles, and FIGS. 7D to 7F are viewsillustrating results obtained by measuring diameters of 200 loaded Pdnanoparticles. Here, FIGS. 7A and 7D illustrate the results of thesample prepared by adding 0.5 ml (0.50 μmol) of K₂PdCl₄ in Example,FIGS. 7B and 7E illustrate the results of the sample prepared by adding0.5 ml (0.75 μmol) of K₂PdCl₄ in Example, and FIGS. 7C and 7F illustratethe results of the sample prepared by adding 0.5 ml (1.0 μmol) ofK₂PdCl₄ in Example. It was confirmed that in the case in which 0.50 μmolof K₂PdCl₄ was added, the Pd nanoparticles had a size in a range of1.7±0.2 nm, in the case in which 0.75 μmol of K₂PdCl₄ was added, the Pdnanoparticles had a size in a range of 1.9±0.2 nm, and in the case inwhich 1.0 μmol of K₂PdCl₄ was added, the Pd nanoparticles had a size ina range of 3.1±0.3 nm. However, it was confirmed that in the case inwhich 2.0 μmol or more of K₂PdCl₄ was added, an aggregate in which thepolymer capsules were aggregated together with the Pd nanoparticles wasprepared.

As illustrated in FIGS. 7A to 7F, it may be appreciated that the size ofthe Pd nanoparticles to be loaded may be adjusted by the amount of thewater-soluble transition metal precursor. In addition, it may beappreciated that when the number of moles of the added water-solubletransition metal precursor was 1 to 4 times based on a total number ofmoles of the compound represented by Chemical Formula 1, used at thetime of preparing the polymer capsule, individual polymer capsulesloaded with the Pd nanoparticles in a state in which the Pdnanoparticles were spaced and dispersed apart from each other may beprepared.

FIGS. 8A and 8C are a high-magnification TEM photograph of the preparedpolymer capsule (FIG. 8A) loaded with Au nanoparticles and a viewillustrating a result obtained by measuring a diameter of the loadedtransition metal nanoparticles (Au nanoparticles), respectively, andFIGS. 8B and 8D are a high-magnification TEM photograph of the polymercapsule loaded with Pt nanoparticles, and a view illustrating a resultobtained by measuring a diameter of the loaded transition metalnanoparticles (Pt nanoparticles), respectively. It may be confirmed thatthe loaded Au nanoparticles had a size in a range of 2.1±0.4 nm, and theloaded Pt nanoparticles had a size in a range of 1.8±0.3 nm, such thatthe transition metal nanoparticles having a significantly uniform sizewere loaded, similarly to Pt.

In order to confirm stability of the transition metal nanoparticlesloaded on the prepared polymer capsule in water and heterogeneouscatalytic activity thereof, a Suzuki-Miyaura reaction in water and aBuchwald-Hartwig amination reaction in a mixed solution of water andtetrahydrofuran (THF) were conducted. It was confirmed that at the timeof using prepared polymer capsule loaded with Pd nanoparticles as acatalyst, and using C₆H₅I and 4-(MeO)C₆H₄B(OH)₂ or C₆H₅I and4-(MeO)C₆H₄NH₂, a conversion rate of aryl iodide (C₆H₅I), which is areactant, was 100%, respectively. In the case of the Suzuki-Miyaurareaction (C₆H₅I and 4-(MeO)C₆H₄B(OH)₂), the conversion rate by thereaction in water at room temperature for 1 to 2 hours was measured, andthe results are illustrated in the following Table 1. The conversionrate of aryl iodide was measured using gas chromatography-massspectrometry (GC-MS).

TABLE 1 entry Ar-X ArB(OH)₂ or ArNH₂ Catalyst Conversion (%) 1 C₆H₅I4-(MeO)C₆H₄B(OH)₂ 3 100% (1^(st) run) 2 C₆H₅I 4-(MeO)C₆H₄B(OH)₂ 3 100%(2^(nd) run) 3 C₆H₅I 4-(MeO)C₆H₄B(OH)₂ 3 100% (3^(rd) run) 4 C₆H₅I4-(MeO)C₆H₄B(OH)₂ 3 100% (4^(th) run) 5 C₆H₅I 4-(MeO)C₆H₄B(OH)₂ 3 100%(5^(th) run) 6 C₆H₅I 4-(MeO)C₆H₄B(OH)₂ Pd/C  62% 7 C₆H₅I 4-(MeO)C6H4NH23 100%

In Table 1, number 3 in the catalyst category indicates a case in whichthe prepared polymer loaded with Pd nanoparticles was used as thecatalyst, and Pd/C in the catalyst category indicates a case in which aPd/C catalyst (purchased from Aldrich in) in which 10 wt % of Pd isloaded on carbon was used.

FIG. 9 is a view illustrating a result obtained by measuring aconversion rate of aryl iodide using the prepared polymer capsule loadedwith Pd nanoparticles depending on a reaction time. As illustrated inFIG. 9, it may be appreciated that the conversion rate reached 100%after about 90 minutes or so.

Hereinabove, although the present invention is described by specificmatters, exemplary embodiments, and drawings, they are provided only forassisting in the entire understanding of the present invention.Therefore, the present invention is not limited to the exemplaryembodiments. Various modifications and changes may be made by thoseskilled in the art to which the present invention pertains from thisdescription.

Therefore, the spirit of the present invention should not be limited tothe above-described embodiments, and the following claims as well as allmodified equally or equivalently to the claims are intended to fallwithin the scope and spirit of the invention.

The invention claimed is:
 1. A polymer capsule loaded with transitionmetal particles comprising: a surface-modified polymer capsule in whicha surface of a polymer capsule is modified with CH₃I; and Pd particlesloaded on a surface of the surface-modified polymer capsule, wherein thepolymer capsule is obtained by copolymerizing a compound represented bythe following Chemical Formula 3 and 3,6-dioxa-1,8-octanedithiol witheach other, and the surface-modified polymer capsule has a positive zetapotential in a dispersed state in water: